1. Feeding enriched diets, i.e., those high in vitamins, minerals and fat to 23-month old male mice failed to defer the loss of body weight associated with senescence, and shortened the remaining life span by 20%. 2. Diets containing 50% cellulose markedly increased the life span of mice whereas those containing 33% cellulose were only minimally beneficial. This is the result of an apparent adequate compensatory increased food intake by animals fed the latter diet. The cellular protein synthesis of the liver of animals fed both levels of cellulose were reduced approximately 30%. 3. Continued studies confirm earlier observations that the life span of genetically determined diabetic mice is markedly increased by feeding an adequate diet intermittently, or a diet low in protein. In addition, although the addition of 50% cellulose to an adequate diet did not increase the life span of diabetic mice, reducing the cellulose to 33% of the diet was the most effective dietary manipulation to increase the life span of these animals.